Nanoimprint lithography has attracted growing attention in recent years as the integration of semiconductor devices increases or various devices become more miniaturized. The nanoimprint lithography provides a method of forming nanometer-sized patterns. Typically, in nanoimprint lithography, a template (mold), which has predetermined topological patterns, is pressed onto a silicon wafer on which an imprint resist is provided, thereby transferring the patterns in the imprint resist on the silicon wafer. By way of this, patterns can be transferred with a high accuracy of size control and with an excellent reproducibility of pattern designs.
Accordingly, even a very small contaminant adhering to the mold would cause the resulting pattern to undesirably contain the shape of the contaminant, which results in defects in the pattern. In order to improve the yield of semiconductor devices and ensure a high reliability thereof, molds need to be cleaned so as to be free from the adhesion of contaminants.
One of potential methods of cleaning molds would be ultrasonic cleaning. However, in ultrasonic cleaning, generated ultrasonic cavitation itself as well as vibration of removed contaminant particles might damage the surface of a mold having nanofabricated patterns. Another potential method would be a method of removing contaminant particles by dissolving the contaminant particles with an acid or alkali solution. However this method requires the selection of a solution that does not react with an object to be cleaned, and thus such a method is not widely applicable.